1. Field of the Invention
The invention relates to a wood planing machine, more particularly to a portable wood planing machine having a locking mechanism for locking a carriage and an adjustment mechanism for adjusting the height of the carriage from a base.
2. Description of the Related Art
Various forms of wood planing machines have existed in the art. FIG. 1 shows a portable planing machine 10 which is disclosed in U.S. Pat. No. 5,771,949. The planing machine 10 has an upper carriage 11 which is mounted on a lower base 14 via two pairs of upstanding posts (not shown) provided at two sides of the base 14 and which is slidable along the posts to move upward and downward. The carriage 11 carries a workpiece planing element, and the base 14 serves to support a workpiece to be formed or planed by the workpiece planing or forming element. At each side of the base 14 is provided an upstanding screw rod (not shown) between each pair of the upstanding posts. The screw rods at two sides of the base 14 pass through the carriage 11 and can be turned by operating an operating lever 121. When the screw rods are turned, the carriage 11 is moved upward or downward, thus adjusting a gap between the carriage 11 and the base 14, which determines the thickness of the workpiece formed by the machine 10. A locking mechanism for locking the carriage against movement relative to the upstanding posts of the base 14 includes two pairs of linkage assemblies 15 each of which is disposed between two adjacent upstanding posts at one side of the carriage 11. Each linkage assembly has a pair of pivotally interconnected linkage members and two clamp members attached to the linkage members. When the linkage assembly is in a stretched position, the clamp members are moved outward so that they abut against the upstanding posts and push the same to the corresponding bearing members (not shown), thus clamping the upstanding posts against the bearing members. Such linkage assembles are found to be disadvantageous in that, when the planing machine vibrates during operation, the pivotally interconnected linkage members may accidentally collapse and move the clamp members away from their clamping positions. On the other hand, as the upstanding posts hold the carriage 11 by passing through socket members integrally formed with the carriage, the walls of the socket members are subjected to clamping forces which are applied to the upstanding posts. These clamping forces are applied in directions from an inner side of the carriage 11 to an outer side thereof. Since the socket members and outer structural members of the carriage 11 generally have less thickness and strength as compared to those situated at the inner side of the carriage 11, the carriage 11 tends to wear and break at the outer sides thereof due to the frequently applied outward clamping forces.
The planing machine 10 further has an adjustment mechanism for adjusting the gap between the carriage 11 and the base 14. The adjustment mechanism comprises a rotary adjustment member which is mounted on the base and which is selectively movable among a plurality of operating positions. The rotary adjustment member has a plurality of screw members arranged annularly at intervals and projecting upward to different heights. When the carriage 11 moves downward and contacts one of the screw members, the carriage 11 is stopped at the height of the screw member contacted therewith. A drawback in this adjustment mechanism is that the number of the annularly arranged screw members is limited by the diameter of the rotary adjustment member which is disposed in a limited space of the planing machine.